Line

The Line element is used to model most multi-phase, two-port lines or cables. It is a “Pi” model with shunt capacitance. This is a Power Delivery element described by its impedance. Impedances may be specified by symmetrical component values or by matrix values. Alternatively, you may simply refer to an existing LineCode object from which the impedance values will be copied. Or you may specify an existing Geometry object and the line impedances will be computed.

You can define the line impedance at a base frequency directly in a Line object definition or you can import the impedance definition from a LineCode object. Both of these definitions of impedance are quite similar except that the LineCode object can perform Kron reduction. (See LineCode Object).

If the Geometry property is specified, all previous definitions are ignored. The DSS will compute the impedance matrices from the specified geometry each time the frequency changes.

Whichever definition is the most recent applies, as with nearly all DSS functions.

Note the units property; you can declare any length measurement in whatever units you please. Internally, everything is converted to meters. Just be sure to declare the units. Otherwise, they are assumed to be compatible with other data or irrelevant.

The default Line object is a 1000-ft overhead line with 336 MCM ACSR conductor on a 8-ft crossarm. It is defined by symmetrical component values:

R1 = 0.0580 ohms per 1000 ft

X1 = 0.1206 ohms per 1000 ft

R0 = 0.1784 ohms per 1000 ft

X0 = 0.4047 ohms per 1000 ft

C1 = 3.4e-9 nF per 1000ft

C0 = 1.6e-9 nF per 1000ft

The corresponding values of Rg and Xg for Rho=100 and 60 Hz are:

Rg = 0.01805 ohms per 1000 ft

Xg = 0.155081 ohms per 1000 ft

The properties, in order, are:

bus1	Name of bus for terminal 1. Node order definitions optional.
bus2	Name of bus for terminal 2
Linecode	Name of an existing LineCode object containing impedance definitions.
Length	Length multiplier to be applied to the impedance data.
Phases	No. of phases. Default = 3. A line has the same number of conductors per terminal as it has phases. Neutrals are not explicitly modeled unless declared as a “phase”, and the impedance matrices must be augmented accordingly. For example, a three-phase line has a 3x3 Z matrix with the neutral reduced, or a 4x4 Z matrix with the neutral retained.

Symmetrical Component Impedance Definition Properties

If any of the following properties are used, the Line object primitive Y matrix is computed using the present values of the other symmetrical component line properties. This is the default method. One limitation to using the symmetrical component method is you can’t correctly represent asymmetrical line constructions. Use the matrix properties or the Geometry property to overcome this limitation.

R1	positive-sequence resistance, ohms per unit length.
X1	positive-sequence reactance, ohms per unit length.
R0	zero-sequence resistance, ohms per unit length.
X0	zero-sequence reactance, ohms per unit length.
C1	positive-sequence capacitance, nanofarads per unit length. Setting any of R1, R0, X1, X0, C1, C0 forces the program to use the symmetrical component line definition. See also Cmatrix and B1
C0	zero-sequence capacitance, nanofarads per unit length.
B1	Alternate way to enter C1, microS per unit length.
B0	Alternate way to enter C0, microS per unit length.
Normamps	Normal ampacity, amps.
Emergamps	Emergency ampacity, amps. Usually the one-hour rating.
Faultrate	Number of faults per year per unit length. This is the default for this general line construction.
Pctperm	Percent of the faults that become permanent (requiring a line crew to repair and a sustained interruption).
Repair	Hours to repair.
BaseFreq	Base Frequency at which the impedance values are specified. Default = 60.0 Hz.

Matrix Impedance Definition Properties

You may define line impedances in a Line object definition using matrices. If you use any of the following properties and do not supercede it with a symmetrical component property or either a LineCode or Geometry property, the primitive Y matrix is computed assuming you wish to use the quantities defined through the matrix properties below. The default matrix values correspond to the symmetrical component defaults described above. The remain at those values until you change them. Matrix properties allow you great flexibility in modeling all sorts of line asymmetries. If you will be solving at some frequency other than the base frequency, be sure to define Rg and Xg (see LineCode object description).

R1	positive-sequence resistance, ohms per unit length.
X1	positive-sequence reactance, ohms per unit length.
R0	zero-sequence resistance, ohms per unit length.
X0	zero-sequence reactance, ohms per unit length.
C1	positive-sequence capacitance, nanofarads per unit length. Setting any of R1, R0, X1, X0, C1, C0 forces the program to use the symmetrical component line definition. See also Cmatrix and B1
C0	zero-sequence capacitance, nanofarads per unit length.
B1	Alternate way to enter C1, microS per unit length.
B0	Alternate way to enter C0, microS per unit length.
Normamps	Normal ampacity, amps.
Emergamps	Emergency ampacity, amps. Usually the one-hour rating.
Faultrate	Number of faults per year per unit length. This is the default for this general line construction.
Pctperm	Percent of the faults that become permanent (requiring a line crew to repair and a sustained interruption).
Repair	Hours to repair.
BaseFreq	Base Frequency at which the impedance values are specified. Default = 60.0 Hz.

Matrix Impedance Definition Properties

Rmatrix	Series resistance matrix, ohms per unit length. See Command Language for syntax. Lower triangle form is acceptable.
Xmatrix	Series reactance matrix, ohms per unit length.
Cmatrix	Shunt nodal capacitance matrix, nanofarads per unit length.
Switch	{y/n \| T/F} Default= no/false. Designates this line as a switch for graphics and algorithmic purposes. SIDE EFFECT: Sets R1=0.001 X1=0.0. You must reset if you want something different.
Rg	Carson earth return resistance per unit length used to compute impedance values at base frequency. For making better frequency adjustments. Applies to line impedances defined using the Line object properties described here or to impedances defined by LineCode objects. Does not apply to impedances defined by Geometry. See explanation in LineCode object. Default values are same as for default LineCode object, which corresponds to the default Line object impedances. Set both Rg and Xg = 0 if you do not wish for earth return correction to be adjusted when the frequency of the solution is different than the base frequency.
Xg	Carson earth return reactance per unit length used to compute impedance values at base frequency. For making better frequency adjustments. Applies to line impedances defined using the Line object properties described here or to impedances defined by LineCode objects. Does not apply to impedances defined by Geometry. See explanation in LineCode object. Default values are same as for default LineCode object, which corresponds to the default Line object impedances. Set both Rg and Xg = 0 if you do not wish for earth return correction to be adjusted when the frequency of the solution is different than the base frequency.
Rho	Earth resistivity used to compute earth correction factor. Overrides Line geometry definition if specified. Default=100 meter ohms.
Geometry	Geometry code for LineGeometry Object. Supercedes any previous definition of line impedance. Line constants are computed for each frequency change or rho change. CAUTION: may cause the number of phases to be redefined.
EarthModel	One of {Carson \| FullCarson \| Deri}. Default is the global value established with the Set EarthModel option. See the Options Help on EarthModel option. This is used to override the global value for this line. This option applies only when the "geometry" property is used.
Units	Length Units = {none \| mi \| kft \| km \| m \| Ft \| in \| cm } Default is None - assumes length units match impedance units.
Seasons	Defines the number of ratings to be defined for the wire, to be used only when defining seasonal ratings using the "Ratings" property.
Ratings	An array of ratings to be used when the seasonal ratings flag is True. It can be used to insert multiple ratings to change during a QSTS simulation to evaluate different ratings in lines.
LineType	Code designating the type of line. One of: OH, UG, UG_TS, UG_CN, SWT_LDBRK, SWT_FUSE, SWT_SECT, SWT_REC, SWT_DISC, SWT_BRK, SWT_ELBOW. OpenDSS currently does not use this internally. For whatever purpose the user defines. Default is OH.
Like	Name of an existing Line object to build this like.

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